Fingerprints have been conventionally recorded by the application of an individual's finger to an ink pad and then applying the inked finger to a record sheed to reproduce the fingerprint pattern on the record sheet. The more sophisticated fingerprint sensing, recording and identification techniques usually resort to devices based on optical techniques for this purpose. The majority of the identification systems based on optical fingerprint sensing and acquisition provide a fairly precise image of the fingerprint but they appear to suffer from the contamination of the sensor by the finger oils, perspiration, etc. One optical system known to me that overcomes this problem is described in U.S. Pat. No. 4,322,163. The optical system described in U.S. Pat. No. 4,322,163 overcomes the problems of prior art optical sensors by introducing a deformable mirror membrane into the device for sensing the finger pattern. It appears, however, that the optical system disclosed in the U.S. Pat. No. 4,322,163 patent also has some disadvantages, such as the requirement for movable mechanical elements, fragile optical elements and a gas laser. All of these devices lower the reliability, increase the physical size, and increase the cost of such optical fingerprint sensing systems. Moreover, the optical information gained from the deformable mirror, as disclosed in the U.S. Pat. No. 4,322,163 is intrinsically analog, that is, ambiguities may be present in the signals . This problem is apparent in any optically based direct fingerprint acquisition system.
There are also presently known electrical techniques for sensing fingerprints and converting the fingerprint pattern to electrical signals. Some of these are disclosed in U.S. Pat. Nos. 4,353,056 and 4,394,773. The devices seem to be either highly theoretical devices, or devices that have not been introduced into the marketplace and therefore appear to suffer from the lack of practical implementation. Other electrical techniques have been developed for touch sensing, including for use in conjunction with robotics. Most of these robotic devices are either too complex or have too low a resolution to be employed for sensing fingerprint patterns. Accordingly, there is a present need for an improved, reliable, and low cost fingerprint sensor that will convert the ridges and valleys of an individual's finger pattern to electrical signals to allow the electrical signals to be processed by known computer techniques or other well known fingerprint identification techniques. Preferably, the electrical signals that are generated in transforming the fingerprint pattern are strictly digital signals, thus minimizing any sensing ambiguities.